1. Field of the Invention
This invention relates to a material container and method of making same. The invention further relates to a liner for a molten metal container. Particularly, the invention relates to containers and liners for holding molten aluminum-lithium alloys.
2. Description of the Prior Art
When making, treating, transporting or otherwise handling certain materials, including corrosive molten metals, it often becomes necessary to hold such materials in a vessel capable of withstanding extreme temperatures and harsh chemical conditions for extended periods of time. Containers made from such substances as silica, calcium silicate and aluminum silicate are used for handling many aluminum alloy melts. Such components have porosities which cause them to at least partially absorb the molten metal in contact with the container, however. To inhibit such absorption, it is known to provide porous refractories with a protective silicon carbide-based coating as in U.S. Pat. No. 4,429,003 and block the flow of oxidizing gases into the refractory's internal phases. Should a portion of coating layer flake or spall off, more deeply deposited carbide particles will oxidize and renew the protective sealing layer.
It is further known to manufacture molten metal container tiles from a mixture of zirconium oxide, neodymium oxide, aluminum oxide and between 8-14% by weight lithium oxide. Tiles made from such mixtures as disclosed in Russian Pat. No. 767,069 are supposedly more heat resistant.
When lithium is added to molten aluminum, other metal handling complications arise. Because lithium increases the oxidation rate of most metals to which it is alloyed, aluminum-lithium generally contaminates or corrodes many refractory substances in contact therewith. A graphite container, for example, self-destructs when exposed to an aluminum-lithium melt. As lithium depletes from the molten alloy and penetrates pores and cracks in the container, the original container interior begins to swell and spall away in a matter of hours, thereby exposing more of the container structure to corrosive metal attack.
Commercially preferred sizes of molten metal containers are usually made from a plurality of blocks or bricks joined with mortar. Such assemblies are not available for aluminum-lithium containment, however, unless both the blocks and mortar withstand prolonged molten metal attack. In U.S. Pat. No. 4,581,295, there is disclosed a refractory assembly for containment of molten aluminum-lithium. The bricks of this assembly consist of silicon carbide with a bonding agent (silicon nitride or silicon oxynitride) dispersed throughout. The mortar mix comprises a particulate nitride filler, colloidal sol binder and less than 2% by weight of a magnesium, calcium, chromium or manganese oxide or hydroxide. In a preferred embodiment, up to 20% boron nitride is added to the mortar to make it non-wetting with respect to the contained molten alloy. Such containment materials are not perfect, however, as evidenced by the amount of silicon the alloy absorbs at FIG. 4.
It is further known to treat refractories with a fluoride-bearing material which is not wetted by molten aluminum. In European patent Application No. 165,754, there is disclosed a method for applying magnesium fluoride (MgF.sub.2) to articles made from alumina, silica, calcium silicate, and especially aluminum silicate, for enhancing their resistance to molten aluminum-magnesium attack. The above reference also states that the same or similar compounds may be used with lithium-containing aluminum alloys. However, at Example 1, page 27, treated and non-treated tubes are only exposed to an Al-0.5% Mg alloy containing 30 ppm Li (and 50 ppm Na). Such trace amounts do not typically qualify as an aluminum-lithium alloy. In addition, thermodynamic calculations indicate that such coatings would not be stable when exposed to greater quantities of lithium. Although capable of withstanding attack by aluminum-magnesium melts, MgF.sub.2 coatings should slowly dissolve in the presence of a true aluminum-lithium melt.
It is still further known to manufacture sintered sheet electrolyte holders for fused salt fuel cells from a slurry of lithium aluminate powder, methanol solvent, dibutyl phthalate plasticizer and polyvinyl alcohol binder. Exemplary of such manufacturing methods is that disclosed in Japanese Pat. No. 59/217,957.